This invention generally relates to the field of digitally controlled printing devices, and in particular to liquid ink printheads which integrate multiple nozzles on a single substrate and in which a liquid drop is selected for printing by thermo-mechanical means.
Ink jet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because, e.g., of its non-impact, low noise characteristics and system simplicity. For these reasons, ink jet printers have achieved commercial success for home and office use and other areas.
Ink jet printing mechanisms can be categorized as either continuous (CIJ) or Drop-on-Demand (DOD). U.S. Pat. No. 3,946,398, which issued to Kyser et al. in 1970, discloses a DOD ink jet printer which applies a high voltage to a piezoelectric crystal, causing the crystal to bend, applying pressure on an ink reservoir and jetting drops on demand. Piezoelectric DOD printers have achieved commercial success at image resolutions greater than 720 dpi for home and office printers. However, piezoelectric printing mechanisms usually require complex high voltage drive circuitry and bulky piezoelectric crystal arrays, which are disadvantageous in regard to number of nozzles per unit length of printhead, as well as the length of the printhead. Typically, piezoelectric printheads contain at most a few hundred nozzles.
Great Britain Patent No. 2,007,162, which issued to Endo et al., in 1979, discloses an electrothermal drop-on-demand ink jet printer that applies a power pulse to a heater which is in thermal contact with water based ink in a nozzle. A small quantity of ink rapidly evaporates, forming a bubble, which causes a drop of ink to be ejected from small apertures along an edge of a heater substrate. This technology is known as thermal ink jet or bubble jet.
Thermal ink jet printing typically requires that the heater generates an energy impulse enough to heat the ink to a temperature near 400xc2x0 C. which causes a rapid formation of a bubble. The high temperatures needed with this device necessitate the use of special inks, complicates driver electronics, and precipitates deterioration of heater elements through cavitation and kogation. Kogation is the accumulation of ink combustion by-products that encrust the heater with debris. Such encrusted debris interferes with the thermal efficiency of the heater and thus shorten the operational life of the printhead. And, the high active power consumption of each heater prevents the manufacture of low cost, high speed and page wide printheads.
U.S. Pat. No. 4,346,387, entitled METHOD AND APPARATUS FOR CONTROLLING THE ELECTRIC CHARGE ON DROPLETS AND INK JET RECORDER INCORPORATING THE SAME, issued in the name of Carl H. Hertz on Aug. 24, 1982, discloses a CIJ system. Such a system requires that the droplets produced be charged and then deflected into a gutter or onto the printing medium. The charging and deflection mechanisms are bulky and severely limit the number of nozzles per printhead.
U.S. Pat. No. 5,739,831, entitled ELECTRIC FIELD DRIVEN INK JET PRINTER HAVING A RESILIENT PLATE DEFORMED BY AN ELECTROSTATIC ATTRACTION FORCE BETWEEN SPACED APART ELECTRODES, issued to Haruo Nakamura on Apr. 14, 1998, discloses an electric field drive type printhead that applies an external laser light through a transparent glass substrate. The laser light strikes a photo conductive material causing it to become conductive thus completing the electrical path for the electrical field. Completion of the electrical path causes the electrical field to collapse around individual segments. These segments are in a deformed state due to their electromechanical response to the applied electric field. The individual segments in contact with a body of ink relax causing a volume of ink to issue from a nozzle plate. This type of printhead requires very high voltages to create the electric field. It also requires very complex laser and mirror systems to control the electric field. These factors prevent the manufacture of low cost, high speed, page wide printheads.
U.S. Pat. No. 5,880,759 entitled LIQUID INK PRINTING APPARATUS AND SYSTEM, issued in the name of Kia Silverbrook on Mar. 19, 1999 and Commonly assigned U.S. patent application Ser. No. 08/954,317 entitled CONTINUOUS INK JET PRINTER WITH ASYMMETRIC HEATING DROP DEFLECTION filed in the names of James Chwalek, Dave Jeanmaire and Constantine Anagnostopoulos on Oct. 17, 1997 and now issued as U.S. Pat. No. 6,079,821, on the other hand, disclose liquid printing systems that afford significant improvements toward overcoming the prior art problems associated with the number of nozzles per printhead, printhead length, power usage and characteristics of useful inks. However, these systems disclose printheads that are fabricated using VLSI silicon technology. Because of the circular geometry of the silicon wafers and limit on their maximum diameter, currently 12xe2x80x3 for state of the art facilities, there is a limit on the maximum length monolithic printheads can be fabricated and manufactured economically.
Each of the described ink jet printing systems has its advantages and disadvantages. However, there remains a widely recognized need for an improved ink jet printing system, providing advantages for example, as to cost, size, speed, quality, reliability, small nozzle orifice size, small droplet size, low power usage, simplicity of construction and operation, durability, and manufacturability. In this latter regard, there is a particular long standing need for the capability to manufacture page wide, high resolution ink jet printheads on a single substrate to overcome the current size limitations associated with silicon wafers. As used herein, the term xe2x80x9cpage widexe2x80x9d refers to printheads of a minimum length of about 4xe2x80x3 and maximum length of about 17xe2x80x3. High resolution implies nozzle density, for each ink color, of a minimum of around 300 nozzles per inch to a maximum of around 2400 nozzles per inch.
In an unrelated field to ink jet print systems are liquid crystal displays (LCD). LCDs are the dominant flat panel display technology for use in laptop computers, hand-held games, and personal digital assistants (PDAs). LCD displays are constructed using thin film transistor (TFT) technologies. Thin film transistors are typically constructed on glass substrates. Typical sizes for glass substrates vary from 0.5xe2x80x3 per side up to, but not limited to, 15xe2x80x3 per side. There are different methods for constructing thin film transistors on glass substrates. Reference for instance, the article by A. Lewis, V. Da Costa, R. Martin, xe2x80x9cPoly-Si TFT Driver Circuits for a-Si TFT-AMLCDs, SID 94 Digest, 1994, pp 251-253, which discloses construction of a 13 inch diagonal LCD using poly-silicon TFTs. Reference also T. Sakurai, K. Kawai, Y. Katoaka, N. Kondo, K. Hashimoto, M. Katayama, T. Nagayasu, Y. Nakata, S. Mizushima, K. Yano, xe2x80x9c11.8 and 10.4 inch diagonal Color TFT-LCDs with XGA Compatibility, xe2x80x9cSID 93 Digest, 1993, pp. 463-466, wherein 10.4 inch and 11.8 inch diagonal color LCDs were fabricated using amorphous silicon (a-Si) TFT technology. Still further, reference P.M. Fryer, et al., xe2x80x9cA Six Mask TFT-LCD Process Using Copper-Gate Metallurgy,xe2x80x9d SID 96 Digest, 1996, pp. 333-336, wherein fabrication of a 10.5 inch diagonal display using amorphous based thin film transistor technology is disclosed. Finally, reference Y. Morimoto et al, of Sanyo Electric Co. LTD., xe2x80x9cA 2.4-in Driver-Integrated Full-Color Quarter VGA (320X3X240) Poly-Si TFT LCD by a Novel Low Temperature Process Using a Combination of ELA and RTA technology,xe2x80x9d IEEE-IEDM Tech. Dig., 1995, pp. 837-840.
All of the above-referenced articles use different processes to form TFTs in order to create control circuitry on a glass substrate. These circuits include, but are not limited to, shift registers, drivers, and logic gates. These examples show that large (about 4 inches or greater) substrates are suitable for constructing digital control circuitry.
Thus, what is required is the capability for the formation of an ink jet printhead using a non-silicon substrate having a large width dimension so as to overcome the problem of size limitations of previous printhead constructions utilizing silicon wafer substrates.
An advantage of the present invention is the improved fabrication of page wide ink jet printheads, of the type for example described by Silverbrook in U.S. Pat. No. 5,880,759 or Chwalek et al, in U.S. Pat. No. 6,079,821, but using substrates other than semiconductive silicon wafer substrates to solve the problem of printhead width limitations.
The present invention therefore principally resides in, among other features, the provision of a particular ink jet printhead design comprising, inter alia, a substrate of a material selected from the group consisting of glass, metal, ceramic or plastic, the substrate having a front surface and at least partially defining an ink holding chamber. The printhead also includes a nozzle plate structure disposed on the front surface of the substrate, the nozzle plate structure being composed of any number of layers of conducting, semi-, and non-conducting material and defining a plurality of ink ejecting orifices therethrough communicating with the ink holding chamber. The nozzle plate structure additionally includes a corresponding actuating element for each ink ejecting orifice. The actuating element is preferably a heater, controllably operable for causing, in DOD type devices, a quantity of ink held in the ink holding chamber to be ejected through the ink ejecting orifice. In CIJ devices, the heaters serve to break up the jet stream of ink into a synchronous array of droplets and to deflect the ink stream.
In one preferred aspect of the invention, the printhead additionally includes a mechanical actuator or actuators controllably operable for exciting or oscillating the ink in the holding chamber to lift the ink to the heaters for facilitating ejection.
A feature of the present invention is the provision of a substrate of a metal, such as stainless steel, or of ceramic or of glass, or resinous material such as polyimide which is larger in surface extent than currently used silicon wafers, such that the printhead can have a continuous extent or width of as much as 17xe2x80x3 or larger, if it is needed.
Another feature of the present invention is the provision of actuating elements for the heaters operatively controlled by drive circuitry using TFT (Thin Film Transistor) technology or silicon based ASICs (Application Specific Integrated Circuits).
Yet another feature of the present invention is the provision of a nozzle plate made of flexible material to prevent cracking, due to stress, of the long printheads or to enable them to be fitted onto curved surfaces.
These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon reading of the following detailed description when taken in conjunction with the drawings wherein there are shown and described illustrative embodiments of the invention.